| Land use and cover change(LUCC)is the main factor to promote the evolution of ecological quality,and it has attracted considerable attention from all sectors of society.Forest-grass ecotone is sensitive to global climate change,with strong temporal and spatial fluctuation,obvious edge effect and high environmental heterogeneity,and which is a typical region to indicate the change of ecological environment quality.Based on the Landsat images acquired in 1990,2000,2010 and2018(June-August)and limited ground surveys,this analysis used an object-oriented decision tree classification algorithm to map land cover types in the forest-grass ecotone of Greater Khingan Mountains in the past around 30 years,followed by an analysis of land cover transitions.Next,with the help of meteorological data and MODIS images,a Carnegie-Ames-Stanford Approach(CASA)model was implemented to derive the spatio-temporal changes in regional NPP.Afterwards,the change in vegetation coverage from 1990 to 2018 was also extracted from a pixel dichotomy model in combination with Landsat images.Finally,a suite of landscape indices in tandem with a forest fragmentation process model were applied to quantify landscape patterns and forest fragmentation spatial processes in the study area,followed by an intensive discussion of the intrinsic relationships between land cover change and ecological environment quality variations.The main research results were as follows:During the period 1990 to 2018,the forest area in the study area decreased by 63241.11 ha,and the fire scar area dropped by 35214.66 ha.The main driving force contributing to the change was that there were many forest fire damages in 1990-2018,and the forest was destroyed to create fire scars,and then the scars gradually changed into grassland.The grassland area reduced by202201.38 ha,and the grassland degradation problem was still serious.The lost grassland mainly turned into artificial surfaces and wasteland.Cultivated land increased by 297330.12 ha,mainly because the local people reclaimed grassland and turned the grassland into cultivated land in 1990 s.After 2000,the cultivated land area decreased by 26122.14 ha,and the persisting Grain for Green Project was the major reason responsible for this decrease.Wetlands decreased by 52367.13 ha in total,and many wetlands degenerated into grassland and wasteland.The artificial surfaces increased by 48737.79 ha in the past 28 years,among which the area of grassland converting into urban land was the largest.Although the area of wasteland increased on the whole,it first increased and then decreased,and the phenomenon of grassland desertification was gradually improved.The most remarkable feature of land cover change in the study area was the large-scale transformation among grassland,cultivated land,artificial surface and desert.From 2000 to 2018,the annual NPP in the study area showed an overall upward trend.In terms of spatial distribution,NPP increased continuously from southwest to northeast,and the northeast forest area and western grassland increased significantly.Vegetation coverage first decreased and then increased,especially in desert and grassland areas.The characteristics of different levels of vegetation coverage transformation was mainly in adjacent levels,and mainly from low vegetation coverage to high vegetation coverage.The average patch area(MPST)of all land types in the study area decreased,which led to the decrease of landscape integrity in the study area.In addition,for forest fragmentation,all forest fragmentation types(shrinkage,perforation,attrition and fragmentation)in 2010-2018 were much less than those in 1990-2000 and 2000-2010,which indicating a gradually strengthened forest protection initiative.From 1990 to 2018,the change of ecological environment quality caused by the change of land cover in some areas of the forest-grass ecotone in Greater Khingan Mountains showed a trend of both improvement and deterioration.The total area of ecological land such as forest land,grassland and wetland in the study area decreased from 12.61 million ha to 12.2924 million ha(2000),then increased to 12.2937 million ha(2010),and finally decreased slightly to 12.2918 million ha(2018).The proportion of ecological land showed a fluctuating trend of first decreasing,then increasing and then slightly decreasing.The decrease of ecological land area was mainly related to the rapid development of cities and road construction.This is basically consistent with the change of vegetation coverage from 1990 to 2018 and the change of NPP in the forest-grass ecotone in the central part of the study area.The research results can provide scientific suggestions for land use planning and ecological protection in the study area.Policy recommendations: in recent years,the ecological environment of forest-grass ecotone has been gradually improved.It is necessary to continue implementing forest fire prevention,paying attention to vegetation restoration after fire,actively promoting the policy of Grain for Green Project.Additionally,reasonable and scientific grazing,actively responding to various special governance policies issued by the state,and promoting the construction of modern comprehensive transportation system are also compulsory. |
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